Help on upgrading brakes

Scarebird is simplest and cheapest. You might have to grind a bit off the caliper corners to clear your wheels, but an electric grinder is just $14 at Harbor Freight and works fast. Better to grind a cheap GM caliper than molest a purty Wilwood one. Don't fret parts. Just write the PN's down in your car's log and rest assured you will always be able to source the common GM & Toyota parts cheap. You will need to drill a 4"D bolt pattern in the rotor, but Scarebird gives a template or will even provide drilled rotors for a bit extra. The Dr Diff kit and others on ebay ~$550 require replacing your 9" spindle with a 1973+ one. They are simply the later factory disk parts. If you need new ball joints and bushings anyway, that might make sense, otherwise much more work.